1. Field of the Invention
The invention relates to detection of metal impurities in the semiconductor process gases and more particularly immediately at the inlet/outlet of the semiconductor process machine.
2. Description of the Related Art
Trace metal contamination in the Ultra Large Scale Integration manufacturing process ULSI, causes poor electrical property in the devices. Electrical properties of the integrated circuit can be altered by the presence of metal impurities in the process gases used during the manufacturing process of the integrated circuits, even with impurity level as low as 10 ppb or even 1 ppb. Therefore, it is an aim of the present invention to control the metal impurity levels in the process gases below those levels. As the integration of the semiconductor devices are advanced, the requirement for the metal contamination control will become even stricter.
Various methods are known to detect metal impurities in the process gases. A first method known as the bubbling method consists of bubbling the process gases through pure water or a dilute acid solution to trap metal impurities in it. The water or the acid solution is then analysed by ICPAES (Inductively Coupled Plasma Atomic Emission Spectrometry), ICPMS (Inductively Coupled Plasma Mass Spectrometry), and/or GFAAS (Graphite Furnace Atomic Absorption Spectrometry) after the appropriate solution preparation, knows by the man skilled in the art.
A second method known as the hydrolysis method consists of absorbing the process gas to be analyzed into pure water together with metal impurities in the gas and to analyze the resultant solution by ICPAES (Inductively Coupled Plasma Atomic Emission Spectrometry), ICPMS (Inductively Coupled Plasma Mass Spectrometry), and/or GFAAS (Graphite Furnace Atomic Absorption Spectrometry) after appropriate solution preparation, well known by the man skilled in the art.
A third method known as the filtration method consists of passing the gas through a filter to trap metal impurities in the gas, then washing out the trapped metals into a dilute acid solution, and analyzing the solution by ICPAES (Inductively Coupled Plasma Atomic Emission Spectrometry), ICPMS (Inductively Coupled Plasma Mass Spectrometry), and/or GFAAS (Graphite Furnace Atomic Absorption Spectrometry) after appropriate solution preparation.
These various methods are disclosed for example in Proceedings of Technical Conference in Semicon Europe 1992, &lt;&lt;Metals and dopants analysis in electronic specialty gases&gt;&gt; by Martine Carre, which is incorporated herein by a reference.
Semiconductor manufacturing, such as etching, is made by using pure or diluted gases. These gases are usually provided to the semiconductor manufacturer in cylinders which are installed usually in gas cabinets at a remote location from the reactor where semiconductors are manufactured and gas is provided therein through pipings. Most of the semiconductor process gases are either reactive or corrosive and metal contamination can be introduced not only from the source gas in the cylinder but also from various components in the gas delivery system. Therefore, it is desirable that the metal impurities can be monitored and controlled at the immediate inlet of the process machine or reactor (the point of use) rather than at the exit of the gas cylinder in order to know exactly which quantity of the metallic impurities is introduced in the process machine.
Semiconductor process machines are generally placed in a clean room where workers are present. In a monitoring/controlling process at the point of use, as new devices are introduced in the gas delivery pipings, there is an increased risk of leaks and the safety of the workers in the clean room not including the damage to various process, equipment there, can be very serious.
On the other hand, since the required control level of the metal impurities in the process gases are at least in the order of a few ppb or a few tens of ppb, it is desired to avoid metallic materials in the sampling device as much as possible which may in turn, increase the level of metallic impurities. The problem, if using non metallic sampling device, however, is that it is difficult to obtain sufficient pressure resistance and leak tightness with non-metallic materials.